The invention relates to a device for measuring the mass of a medium flowing in a line, in particular the intake air mass of internal combustion engines, in which the device includes a temperature-sensitive measurement instrument that is circulated around by the flowing medium and is disposed in a measurement conduit disposed in the line, and the measurement conduit has deflection elements on the inlet and outlet sides for deflecting the flowing medium.
A device for measuring the mass of a medium flowing in a line can be inferred, for example, from DE 44 07 209 C2 as well as from the published article xe2x80x9cBreakthrough in Reverse Flow Detectionxe2x80x94A New Mass Air Flow Meter Using Micro Silicon Technologyxe2x80x9d by Konzelmann, Hecht, and Lemke, published in SAE TECHNICAL PAPER SERIES No. 950433, 1995. With these devices, it is problematic that the inlet side deflecting elements are embodied and disposed so that the flowing medium is deflected in the direction of the measuring element. Since in many instances, particles or also fluid droplets, e.g. oil or grease droplets, are carried along by the flowing medium, particles or fluid droplets of this kind cannot be prevented from striking the measuring element and damaging it. In particular, a membrane provided for the air mass evaluation can be destroyed. The fluid droplets carried along in the flowing medium can flow beyond the membrane region of the measuring element and can lead to the destruction of the membrane. These impurities can therefore result in the failure of the measuring element and therefore of the entire device for measuring the mass of a medium flowing in a line.
In order to minimize the danger of a failure of the measuring element, DE 44 28 216 A1 has disclosed providing a housing in a heating wire air flow instrument, which housing has a main conduit through which the air flows, a central component which is supported in the main conduit of the housing, an inlet section for the intake of a part of the air flowing through the main conduit, a bypass conduit which is connected to the intake section, and an outlet section for returning the air flowing through the bypass conduit back to the main conduit. Sensor devices are provided in the bypass conduit for measuring the air flowing in the bypass conduit. The bypass conduit contains an upstream serpentine section, with a serpentine conduit on an upstream side of the sensor device, a straight tube section, which is embodied as a straight tube and contains the sensor device, as well as a downstream conduit, which connects the straight tube section to the outlet section. The serpentine tube section makes it possible for impurities of the flowing medium, for example particles or fluid droplets, to collect in the serpentine region due to their inertial mass. In this manner, a portion of the impurities of the flowing medium are in fact kept away from the measuring element, but it is nevertheless problematic that particularly at high impurity levels, a portion of the particles, fluid droplets, and the like nevertheless travels through the serpentine region and reaches the measuring element. Furthermore, with this measuring element, it is problematic that it has a relatively complex design. Moreover, it turns out to be extremely problematic that this measuring element can only be used in a flow direction-dependent manner, i.e. the measurement of the mass of a medium flowing in a line can only take place in one direction; it is not possible for the device to be acted on in a manner that is independent of the direction.
The object of the invention, therefore, is to improve a device of this generic type, which is for measuring the mass of a medium flowing in a line, in such a way that firstly, a practically complete absorption of the impurities carried along by the flowing medium is possible and that it can furthermore be used in a manner that is independent of the direction of fluid flow.
This object is attained according to the invention with a device of the type described at the beginning that is for measuring the mass of a medium flowing in a line, in particular the intake air mass of internal combustion engines, by virtue of the fact that the inlet side and outlet side deflection elements are disposed and embodied as essentially symmetrical to the measuring element disposed at the symmetry point.
The inlet side and outlet side deflection elements that are disposed and embodied as essentially symmetrical with regard to the measuring element result in a symmetrical measurement conduit, which offers the great advantage that measurements can be carried out in two flow directions with the same sensitivity, which is of great advantage for example with regard to the appearance of pulsations occurring in the intake conduit of an internal combustion engine and the detection of these pulsations.
It goes without saying that these advantages can also be executed if the measuring element is not disposed precisely at the symmetry point, but slightly asymmetrically with regard to this symmetry point.
In order to produce a particularly favorable absorption of particles, impurities, and the like carried along in the flowing fluid, in a very advantageous embodiment, the provision is made that at least one particle-absorbing element is disposed on the surface of the wall defining the flow conduit and/or on the surface of the deflection elements, preferably on the wall regions of the flow conduit and/or of the deflection elements, which wall regions deflect the flowing medium.
In a particularly advantageous manner, the disposition of this at least one particle-absorbing element on the deflecting wall regions permits a practically complete absorption of particles, oil droplets, or grease droplets, since due to their inertial mass, these not only collide with the wall elements, but are also absorbed by the particle-absorbing element disposed there.
Purely in principle, a wide variety of embodiments is conceivable with regard to the embodiment of the at least one particle-absorbing element. An exemplary embodiment that is advantageous because it is particularly easy to produce makes the provision that the at least one particle-absorbing element is a particle-absorbing wall coating. In particular in addition to a simple manufacture, this has the particularly great advantage that the particle-absorbing element has a large surface area.
Preferably, the particle-absorbing wall coating is comprised of a gel or an adhesive layer.
A wide variety of embodiments is possible with regard to the embodiment of the deflection elements.
A particularly advantageous embodiment makes the provision that the deflection elements are embodied so that they produce a deflection of the flowing medium by at least 180xc2x0. This permits practically the complete absorption of particles and the like, particularly in connection with the particle-absorbing coating disposed in the deflection regions.
A wide variety of embodiments is conceivable with regard to the symmetrical disposition and embodiment of the deflection elements. An embodiment that is optimal in terms of flow dynamics and is advantageous in particular because it is also easy to produce makes the provision that the deflection elements are embodied so that they constitute an S-shaped flow conduit. The deflection elements are preferably bent into a cylinder shape.
This permits a very large surface area of the particle-absorbing coating, which is disposed in the deflection regions.
In order to produce an optimal flow on the measuring element, for example a turbulent flow of the medium, an advantageous embodiment makes the provision that flow elements are disposed in the flow conduit, which influence the flow dynamics of the flowing medium.
For example, the flow elements can be disposed in the flow conduit in such a way that turbulent flows are produced at the measuring element.
Purely in principle, the embodiment of the flow elements to generate a turbulent flow in the flow conduit can take place in a wide variety of ways.
An advantageous embodiment makes the provision that the flow elements are grating elements disposed in front of the measuring element.
Another advantageous embodiment makes the provision that the flow elements are structures, preferably roughened sections, that are embodied on the surface of the flow conduit, preferably on the surface of the wall elements, and they likewise generate turbulent flows in the region of the measuring element.